Mold apparatus for forming shaped plastic shells

ABSTRACT

Apparatus for manufacturing a multitude of thin walled hollow plastic shells for parts such as automobile door panels, controls and instrument panels from dry thermoplastic powders includes a mold heating chamber with a tube sheet heating assembly operative to provide a hot air flow pattern with a profile which matches the outer profile of one of a plurality of molds that are selectively placed in the mold heating chamber thereby to uniformly heat a casting surface of the mold by an energy efficient process.

This is a division of Ser. No. 063,837 filed 6/19/87, now U.S. Pat. No.4,851,177.

TECHNICAL FIELD

This invention pertains to a method and apparatus for making hollowplastic shells especially suitable for us in automobile trim componentssuch as interior door panels and more particularly to methods andapparatus for processing plastic powder to form shells of differingshape by use of gas heated molds with outer surface shapes correspondingto a selected shell shape.

BACKGROUND ART

The automotive industry has turned to the use of interior trimcomponents such a door panels comprising a polyvinyl chloride shell.See, for example, the trim components disclosed in U.S. Pat. No.3,123,403. The acceptance of such components has been because inter aliathis type of construction permits a wide latitude in styling and color,and grain effects which are most desired particularly in the interiordesign of automobiles.

The current state of the art includes method to form preformed grainedvinyl shells from dry thermoplastic powder particles which are appliedto a heated shell mold from a powder box to form a one piece shell whoseshape will correspond to that of the mold casting surface. Examples ofsuch method and apparatus are set forth in U.S. Pat. Nos. 3,492,307issued Jan. 27, 1970, and 4,623,503 issued Nov. 18, 1986. Other devicesfor heating are set forth in U.S. Pat. Nos. 489,299 issued Jan. 3, 1893;1,763,290 issued Feb. 22, 1916; 2,288,012 issued June 30, 1942;2,869,630 issued Jan. 20, 1959; and 3,372,820 issued Mar. 12, 1968.

None of the aforesaid methods and apparatus for manufacture or resultantmanufacture is directed to a process or apparatus which includes arotational tube sheet operative to heat a multitude of mold shapes in anenergy efficient manner so as to form single piece shells from heatfusable thermoplastic material of differing shape such as interior panelcomponents of an automobile.

STATEMENT OF INVENTION AND ADVANTAGES

In accordance with one aspect of the present invention a process forforming a shaped shell on a mold includes balancing a heating chamber toefficiently heat a variety of mold shapes by selectively shaping theflow pattern of hot air flow into the chamber to match the surfaceprofile of a mold being heated by the hot air flow.

A feature of the process is that the flow pattern is matched to theshape of the outer surface of each mold as it enters the heatingchamber. In a preferred embodiment the flow matching is accomplished byvarying the length of air tubes to correspond to the outer surfaceprofile of the mold.

Another aspect of the present invention is to improve a method forheating the casting surface of a mold which includes the step ofdirecting hot air against the outer surface of the mold by providing ahot air drum with an inlet and a plurality of tube sheets each having aplurality of tubes formed thereon of varying length to define aplurality of outlet profiles adapted to match a plurality of differentmold shapes; and thereafter selectively positioning one of the tubesheet profiles in alignment with the outer surface profile of one of themolds to uniformly raise the temperature of the mold to causethermoplastic material to fuse to form a plastic shell on the mold.

In one method the hot air is directed from one tube sheet to impinge ona matched mold surface profile and the air flow is blocked through theremainder of the tube sheets.

In another method the air flow through the drum is passed through onlyone of the tube sheets while the other of the tube sheets are sealedwithin a feed chamber to block air flow therethrough so as toconcentrate inlet air flow to the drum against a mold profile matched tothe selected one of the tube sheets.

Another feature of the present invention is to improve mold heatingapparatus which includes a heating chamber arranged to receive molds forheating a casting surface thereon by directing hot gas against the outersurface profile of the mold and wherein the molds have a multitude ofouter surface profile shapes and the heating chamber includes accessopenings for selectively locating one of a plurality of molds in theheating chamber and wherein the improvement comprises a hot air drumformed from a plurality of joined tube sheets defining a multi-sidedcylinder with each of the sides having a plurality of tubes formedthereon with variable lengths which define an outlet profile thatcorresponds to one of the multitude of mold shapes and wherein the drumis operated by indexing means to align a selected one of the tube sheetswith a selected one of the molds to match their respective profilesthereby to uniformly heat the mold from a pressurized source of airwithout balancing the heating chamber size to accommodate differing sizeand shape molds.

Another feature is to provide mold heating apparatus of the typeset-forth in the preceding paragraph wherein the drum is located in afeed chamber and sealed with respect to a single outlet from the feedchamber so that the hot drum will be pressurized from a pressurizedsource of heated air so that hot gas will be directed from only aselected one of the tube sheets which is matched with the outer profileof mold located within the heating chamber.

Yet another feature of the invention is to provide apparatus of the typeset-forth above wherein the hot air drum is supported on means forraising and lowering the drum with respect to the chamber to preventinterference between the tubes of a selected tube sheet and a selectedmold as the mold is moved into and out of the heating chamber.

Yet another feature is to provide movable fixture doors to seal theselected tube sheet with respect to the feed chamber whereby the feedchamber will pressurize the hot air indexing assembly.

Still another feature is to configure the aforedescribed drum to havehot air feed from both ends of the drum for even pressurization of thetube array which is selected to heat a selected mold.

Yet another feature of the apparatus set forth in the preceding text isthat means are provided to recover the hot air from an enclosed systemto be reheated for return flow to the selectively positioned hot airdrum.

The aforedescribed system further enables a water cooling station to beused to cool the mold once a thermoplastic shell is cast thereon so thatthe tubes for gas flow can be tailored solely for hot air heatingthereby to reduce the normal hot air cycle time.

In a specific embodiment, the apparatus includes octopus arms whichcarry a plurality of molds with respect to a plurality of processstations. The process stations include a heating chamber with heated airsupplied thereto by means of the indexable hot air drum heater assemblyof the present invention. The octopus arms receive molds of a selectedouter profile shape at a mold loading station. The indexable hot airdrum heater assembly is associated with a heating chamber having aninlet door and an outlet door which open to receive the mold as it isswung into the heating chamber by rotation of the octopus arms. Themulti-sided tube sheet assembly operated in combination with amulti-armed casting unit (the octopus machine) provides custom heatingprofiles for a wide variety of mold shapes which provides manufacturingflexibilty heretofore unachievable.

BRIEF DESCRIPTION OF THE INVENTION

Other advantages and a more complete understanding of the invention willbe apparent to those skilled in the art from the succeeding detaileddescription of the invention and the accompanying drawings thereofwherein:

FIG. 1 is a diagrammatic view of molding apparatus including the presentinvention;

FIG. 2 is a sectional view taken along the line 2--2 of FIG. 1 lookingin the direction of the arrows;

FIG. 3 is a sectional view taken along the line 3--3 of FIG. 1 lookingin the direction of the arrows;

FIG. 4 is a perspective view of an indexable tube sheet assembly inanother embodiment of the present invention;

FIG. 5 is a fragmentary diagrammatic view of the tube sheet assembly ofFIG. 4 shown in association with a heating chamber having movablefixture doors defining a port to position a selected one of the tubesheets with respect to the heating chamber;

FIG. 6 is a sectional view showing the position of the fixture doorsclosed with respect to the selected tube sheet;

FIG. 7 is a sectional view showing the position of the fixture doorsopened with respect to the tube sheet assembly prior to matching a tubesheet with a mold of a selected shape;

FIG. 8 is an enlarged elevational view of the outer surface profile of amold and a matching array of hot air tubes; and

FIG. 9 is a method sequence of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The method and apparatus of the present invention will be described withrespect the manufacture of plastic shells having thin walls of the typefound on the exterior surface of interior trim parts for automotive useincluding but not limited to door panels, consoles, instrument panelsand arm rests.

In the manufacture of such articles, thermoplastic fusable material inthe form of dry plastic particles formed from resins with suitableplasticizers is cast against a mold surface which is heated by suitablemeans such as a jet of hot air. The mold temperature will cause theparticles to fuse together to form a layer on the mold. When the layeris cured it is stripped from the mold to form a thin-walled plastic partwith a shape that corresponds t that of the mold surface.

In mass producing such parts it is desirable to conform the mold heatingchamber to a variety of mold shapes. This requires a balancing of theheating chamber and the air flow rates thereto which will result inenergy efficient and timely increases in the mold temperature to adesired level.

The present invention includes an octopus casting machine 10. Theheating balance is accomplished by use of an indexable hot air tubesheet assembly 20 which is associated with an oven heating system 30operative to selectively heat molds 40 which are inputted at a moldloading station 50 on the octopus casting machine 10.

Referring now FIG. 1, the octopus casting machine 10 includes aplurality of arms 12a-12h (eight in number) which are supported on arotatable base 14 driven by suitable drive means more specifically setforth in U.S. Pat. No. 4,755,333 for Mold Method and Apparatus forPlastic Shells with a common assignee.

Once a selected mold 40 is placed on the mold loading station 50 andtransferred to the octopus machine 10, it is advanced by the machine tothe oven heating system 30. The oven heating system 30 includes a sealedenclosure 16 having an inlet door 18 and an outlet door 19. A sealedslot 22 is provided for movement of the mold 40 into a sealed heatingchamber 24 of the oven heating system 30. As best shown in FIG. 2, theheating chamber 24 is located above a sealed feed chamber 26 in whichthe tube sheet assembly 20 is located.

The tube sheet assembly 20 includes a hot air drum 28 formed by sixseparate tube sheets 32a-32f that define a hexagonally configured outersurface on the drum 28. The drum 28 is supported on a pair of spacedpositioning arms 34 each of which is in the form of a bell crank havingone end 35 connected to an end 36 of the drum 28 and having its otherend 37 connected to the end of piston 38 driven by an air cylinder 42.The air cylinder 42 is controlled in response to movement of a mold 40into and out of the heating chamber 24 to extend or retract the piston38. This action will raise and lower the drum 28 in the feed chamber 26.When the drum is in the lower position shown in solid lines in FIG. 2,it can be rotated by a suitable drive motor 44 and drive train 46 toposition a selected one of the tube sheets 32a-32f into alignment withan inlet port 48 to the heating chamber. The drum 28 is then raised asshown in broken outline form in FIG. 2.

By virtue of the elevator action of the air cylinders 42, the tubesheets are positioned below the port 48 such that a plurality of set ofhot air tubes 52a-52f, disposed respectively on each of the tube sheets,will be located out of the transfer path of the mold 40 is it enters andleaves the heating chamber 24.

The drum 28 has an inlet 54 which is connected to a hot air conduit 56through a sealing collar 58. The collar 58 rides on the inlet 54 to sealit with respect to the outlet 60 from a heater duct 62. The duct 62 hasa control valve 64 disposed therein which is positioned to open andclose communication with the outlet 66 from a blower 68 that pressurizesa source 70 of heated air. The source 70 is heated by a gas burner 72located in a combustion chamber 74. The combustion chamber 74communicates with the blower inlet 76 as shown in FIG. 3. A bypass duct78 is provided with a valve 80 to return air back to the combustionchamber when the valve 64 is closed. The bypass duct 78 alsorecirculates return air from the heating chamber 24 via a duct 82 havinga control valve 84 therein which is closed during recirculation butwhich opens to provide hot air recovery from an enclosed oven system.

In accordance with the present invention each of the molds 40 will havea preselected outer profile as shown in FIG. 8 by reference numeral 86.The shape of each profile 86 is inputted to a controller 85 when a mold40 is loaded on the octopus machine 10. The information is fed tosuitable control means such as shown in the aforedescribed U.S. Pat. No.4,755,333 which will be programmed to concurrently operated the drivemotor 44 to index the drum 28 so as to position one of the plurality ofsets of tubes 52a-52f which has a tube outlet profile 88 whichcorresponds to the profile 86 on the selected mold 40. Consequently jetsof hot air from the outlet profile 88 will impinge uniformly against thematched profile of the mold 40 so as to efficiently and uniformly heatthe mold in a manner which will reduce the time required to heat thecasting surface 89 of the mold 40 to a temperature at which drythermoplastic particles will become fused thereon.

FIG. 9 outlines the method of the present invention which includes thesteps of providing a plurality of molds with different outer profileshapes; providing a hot air drum of the aforedescribed type andindexably supporting it with respect to a mold of a predetermined shape.As shown in FIG. 9 the method thereafter includes the steps of advancinga mold into overlying relationship with a hot air drum to match the tubeprofile with the mold surface profile; directing hot air through aselected tube sheet having a tube outlet profile thereon matched to theouter surface profile of the selected mold; and uniformly increasing thetemperature of the mold casting surface by directing air through thematched air tube outlet profile against the matched mold profile.

The improved method balances the heat capacity of a mold heating systemto each of a plurality of molds as they are selectively positioned in aheating chamber of the heating system. Prior systems only were able tobalance the size of the oven to accommodate a range of tool sizes andshapes and the remainder of the heat balancing was accomplished bygrinding the mold surfaces and providing heat sinks, baffles and othermold adjustments to assure that the differing mold types would beuniformly heated at a rate which would be suitable for a continuousproduction cycle in which one of many mold types were being heated.

Because of the present invention, each mold 40 passing through the ovenheating system 30 will reside in the heating chamber 24 for an optimaltime period. Larger mold profiles will be matched with hot air tubes 52that define a larger profile of tube outlets and smaller profiles willbe matched with hot air tubes 52 that define a smaller matching tubeoutlet profile so as to standardize the mold heating resident time.

Each of the molds 40 will then be advanced from the heating system 30 tosequentially pass through a casting station 90 at which the mold isclamped to a powder box 92 off-loaded onto the octopus machine from apowder box carousel 94. The arm 12 is rotated to cause material from thepowder box to cast onto the heated casting surface 89 of the mold 40.Excess material is returned to the powder box 92 when the mold 40 isinverted.

From the casting station 90 the mold 40 with thermoplastic particlesfused on the casting surface 89 is advanced into a curing oven 96. Oncethe cast material is cured the mold 40 can be moved to filler moldingstation 98 which is described in detail in the aforedescribed 014,754application. The mold 40 alternatively or sequentially can be moved to asecond cure oven 100 or to a water cooling station 102 where the mold 40is cooled so that a heat fused shell in the mold 40 can be removedtherefrom.

The use of a water cooling station means that the indexable tube sheetassembly 20 can be designed specifically for hot air flow against a moldon a matched heat flow/mold profile basis. This enables the tubes to besized to flow only heated air rather than both heating and cooling air.The resultant structure is thus matched both on a profile basis and onan optimized air capacity basis. As a result the molds 40 are heated inminimum of time by the least amount of air flow thereby to conserve theamount of fuel consumed in the heating process.

Referring now to the embodiment in FIGS. 4-7 an indexable tube sheetassembly 104 is shown which is supported in a feed chamber 106 that issealed with respect to opposed air inlets 108, 110 at either end of theindexable tube sheet assembly 104. The inlets 108,110 are connected byrotary joints 112,114 respectively which are joined to a hot air feedloop 115 from a heated air source (not shown).

An oven enclosure 116 includes an air enclosure plate 118, which hasfixture doors 120,122 that are driven by suitable drive means (notshown) between opened (FIG. 6) and closed (FIG. 7) positions withrespect to a selected tube sheet 124. As shown in FIG. 6, tube sheet 124has a tube outlet profile 125 matched to the outer surface profile 126of a mold 127. Mold 127 is located in a heating chamber 128. As in thepreviously described embodiment the hexagonally shaped drumconfiguration is custom-tubed to match the mold configuration fordifferent tools. As each arm of the molding unit moves into the heatingchamber 128 the process controller will condition a drive system 130 torotate the assembly 104 to match the proper heating profile to themold/tool profile. Once the two profiles are matched the doors 120,122are closed. This causes the feed chamber 106 to be pressurized as hotair flows through the two inlets 108,110. The chamber 106 is sealed sothat all the air flow passes through the selected tube sheet against thematched mold. The feed of hot air through both ends of the assembly 104evenly pressurizes the tube array for producing a further matching ofthe heat transfer to the mold.

After the mold 127 is heated it is moved from the heating chamber 128and the next mold tool and tube sheet are matched to continue theprocess. As in the first embodiment such indexing or rotation of thesix-sided tube sheet assembly 104 is synchronized with the operation ofthe casting machine 10 so as to result in a custom heating capabilityheretofore unattainable.

While the process has been described with respect to thin shell castmembers it is equally suited for any mold process in which it isdesirable to precisely match the flow of heated gas against a mold partto uniformly heat a mold surface thereon for molding a part frommaterial placed in the mold. The process is not limited to themanufacture of interior trim parts but is suitable for use in themanufacture of a wide range of product types from a wide range offusable thermoplastic materials.

What is claimed is:
 1. In apparatus for casting plastic shells heatingmold having a casting surface for receiving heat fusable thermoplasticmaterial and an outer surface with a profile that corresponds to theshape of the casting surface, the outer surface heated by hot air flowthereagainst from a tube sheet having a plurality of tubes extendingtherefrom with outlets that define a profile corresponding to that ofthe outer surface of the mold, the outlets discharging into an enclosurehaving a mold heating chamber therein and wherein a plurality of moldsof different outer surface profile are sequentially positioned in theheating chamber to have the casting surface temperature raised to alevel at which the material will adhere to the mold to form a plasticshell thereon, the improvement comprising:means forming a feed chamberhaving a outlet in communication with said heating chamber; a drumsupported in said feed chamber having a plurality of tube sheets formedthereon, each of said tube sheets having a plurality of tubes formedthereon of a predetermined height which define a plurality of tubeoutlets defining an air discharge profile that corresponds to the outersurface profile of molds which are positioned in the heating chamber;means for selectively positioning the drum to index one of said tubesheets into alignment with said feed chamber outlet for matching theprofile of one of the outer surface profiles with the air dischargeprofile of the indexed tube sheet; and means for directing heated airthrough the indexed tube sheet for causing the mold casting surface tobe uniformly heated there across prior to placing heat fusablethermoplastic material thereon.
 2. In the combination of claim 1, ablower, said drum having inlet openings in both ends thereof, meansincluding a rotary joint for connecting said inlets to said blower andmeans for sealing said tube sheets with respect to said feed chamberoutlet to prevent bypassing of air from the outlets of the indexed tubesheet back to the feed chamber.
 3. In the combination of claim 1, meansfor supporting said drum for movement into raised and lowered positionswith respect to said heating chamber, said tube sheets having theoutlets thereof located out of said heating chamber when in the loweredposition for defining an unobstructed path for movement of a selectedmold into the heating chamber.
 4. In the combination of claim 1, ablower, said drum having an inlet, means including a rotary joint forsupporting said drum for rotation with respect to the feeder chamberoutlet and for fluidly connecting said blower to said drum inlet, andmeans for sealing said tube sheets with respect to said chamber outletto prevent bypass of heated air from the outlets of an indexed tubesheet to said feed chamber.